Thiolated gamma-cyclodextrin-polymer-functionalized CeFe3O4 magnetic nanocomposite as an intrinsic nanocatalyst for the selective and ultrasensitive colorimetric detection of triacetone triperoxide.

Explosives are powerful destructive weapons used by criminals and terrorists across the globe and their use within military installation sites poses serious environmental health problems. Existing colorimetric sensors for triacetone triperoxide (TATP) relies on detecting its hydrolysed H2O2 form. However, such detection strategy limits the practicability for on-site TATP sensing. In this work, we have developed a novel peroxidase mimic catalytic colorimetric sensor for direct recognition of TATP. Ceria (Ce)-doped Fe3O4 nanoparticles (CeFe3O4) were synthesized via the hot-injection organic synthetic route in the presence of metal precursors and organic ligands. Thereafter, the organic-capped CeFe3O4 nanoparticles were surface-functionalized with amphiphilic polymers (Amp-poly) to render the nanoparticle stable, compact and biocompatible. Thiolated γ-cyclodextrin (γ-CD) was adsorbed on the Amp-poly-CeFe3O4 nanocomposite (NC) surface to form a γ-CD-Amp-poly-CeFe3O4 NC. γ-CD served both as a receptor and as a catalytic enhancer for TATP. Hemin (H), used as a catalytic signal amplifier was adsorbed on the γ-CD-Amp-poly-CeFe3O4 NC surface to form a γ-CD-Amp-poly-CeFe3O4-H NC that served as a functional nanozyme for the enhanced catalytic colorimetric detection of TATP. Under optimum experimental reaction conditions, TATP prepared in BIS-TRIS-Trisma Ac-KAc-NAc buffer, pH 3, was selectively and ultrasensitively detected without the need for acid hydrolysis based on the catalytic oxidation of 3,3',5,5'-tetramethylbenzidine by H2O2 in the presence of the γ-CD-Amp-poly-CeFe3O4-H hybrid nanozyme. The obtained limit of detection of ∼0.05 µg/mL when compared with other published probes demonstrated superior sensitivity. The developed peroxidase mimic γ-CD-Amp-poly-CeFe3O4-H catalytic colorimetric sensor was successfully applied to detect TATP in soil, river water and tap water samples.

Controlled metallization of ion-exchanged glasses by thermal poling.

We present studies of the formation of silver nanoparticles (NPs) in silver-sodium ion-exchanged glasses by a combination of thermal poling and nanosecond pulsed laser irradiation at 355 nm. In poling, silver ions drift deeper into the glass and become separated from the glass surface by a poled layer depleted in cations. Performed measurements have indicated poling-induced broadening of silver ions depth distribution. Laser irradiation reduces silver ions to atomic silver via breaking silver-non-bridging oxygen (NBO) bonds, extraction of electrons from the NBO atoms and capturing these electrons and electrons generated via multi-photon absorption in the glass by silver ions. The depleted layer limits diffusion of silver atom towards glass surface and, as a consequence, formation of silver NPs on the surface of poled glasses. It is shown that thermal poling mode allows one to control formation of silver NPs of glass surface.

Rapid and highly selective colorimetric detection of nitrite based on the catalytic-enhanced reaction of mimetic Au nanoparticle-CeO2 nanoparticle-graphene oxide hybrid nanozyme.

The International Agency for Research cancer (IARC) has classified nitrite in Group 2A of probable carcinogens to human. Herein, we report on the rapid and selective colorimetric detection of nitrite using a chemically modified gold nanoparticle (AuNP)-cerium oxide (CeO2) NP-anchored graphene oxide (GO) hybrid nanozyme in a catalytic colorimetric assay where nitrite acts as the main oxidant/target analyte and 3,3',5,5'-tetramethylbenzidine (TMB) as the substrate. CeO2 NPs and GO were synthesized separately and incorporated in-situ, in a synthetic solution involving the chemical reduction of Au salt to AuNPs. The chemical modification process aided the adsorption of CeO2 NPs and AuNPs on GO nanosheets, yielding a highly catalytic AuNP-CeO2 NP@GO nanohybrid material. Under optimum experimental conditions, a novel colorimetric assay for nitrite recognition was constructed in which AuNP-CeO2 NP@GO hybrid nanozyme catalysed the oxidation of TMB in the presence of nitrite prepared in a 2-(n-morpholino)ethanesulfonic acid-2-[bis(2-hydroxyethyl)amino]-2-(hydroxymethyl)propane-1,3-diol-tris(hydroxymethyl)aminomethane acetate (MES-BIS-TRIS-Trisma Ac)-citric acid buffer solution, pH 2. Nitrite was quantitatively detected in a concentration dependent manner from 100 µM to 5000 µM with a correlation coefficient of 0.9961 and a limit of detection of 4.6 µM. Selective detection of nitrite was confirmed by the generation of a unique green colour reaction upon nitrite interaction in the AuNP-CeO2 NP@GO hybrid nanozyme redox cycle with TMB. None of the several tested metal ions and including H2O2 yielded a positive colour response, thus demonstrating the superior selectivity of the catalytic colorimetric assay for nitrite recognition. The AuNP-CeO2 NP@GO hybrid nanozyme catalytic colorimetric assay was successfully applied in the detection of nitrite in tap water.

Biomimetic graphene oxide-cationic multi-shaped gold nanoparticle-hemin hybrid nanozyme: Tuning enhanced catalytic activity for the rapid colorimetric apta-biosensing of amphetamine-type stimulants.

Amphetamine-type stimulants are a class of illicit drug that constitutes a worldwide problem to which intelligence agencies, first responders and law enforcement are tasked with identifying them in unknown samples. We report on the development of a graphene oxide (GO)-cationic multi-shaped gold nanoparticle (AuNP)-hemin hybrid nanozyme as a new biomimetic catalytic-induced aptamer-based colorimetric biosensor platform for amphetamine (AMP) and methamphetamine (MAMP). GO was electrostatically bonded to cationic multi-shaped cetyltrimethylammonium bromide (CTAB)-AuNPs to form a GO-CTAB-AuNP hybrid nanozyme exhibiting enhanced catalytic activity in the presence of hemin. The binding of an MNS 4.1 anticocaine DNA aptamer on the GO-CTAB-AuNP-hemin nanozyme assembly and the subsequent catalytic oxidation by 3,3,5,5-tetramethylbenzidine in the presence of H2O2 ensured that the colorimetric reaction was tuned to selectively detect AMP and MAMP with high sensitivity. Under optimum experimental conditions, AMP and MAMP were quantitatively detected within 1 min with a detection limit of 34.1 ng/mL and 28.6 ng/mL respectively. Selected substances and drugs, known to react positively to Marquis and Mandelin reagents (used in AMP and MAMP presumptive testing) and well-known adulterants, were tested for their affinity to react with the aptamer-based GO-CTAB-AuNP-hemin peroxidase mimic biosensor. The deep blue colorimetric reaction, specific to AMP and MAMP detection, was used as the basis to affirm the selectivity of the aptamer-based GO-CTAB-AuNP-hemin peroxidase mimic biosensor. We believe the colorimetric biosensor developed in this work demonstrates a promising new direction in presumptive testing for AMP and MAMP.

Aptamer-based cocaine assay using a nanohybrid composed of ZnS/Ag2Se quantum dots, graphene oxide and gold nanoparticles as a fluorescent probe.

Authors report on a new fluoro-graphene-plasmonic nanohybrid aptamer-based fluorescent nanoprobe for cocaine. To construct the nanoprobe, newly synthesized glutathione-capped ZnS/Ag2Se quantum dots (QDs) were first conjugated to graphene oxide (GO) to form a QD-GO nanocomposite. The binding interaction resulted in a fluorescence turn-ON. Thereafter, cetyltrimethylammonium bromide (CTAB)-gold nanoparticles (AuNPs) were directly adsorbed on the QD-GO nanocomposite to form a novel QD-GO-CTAB-AuNP nanohybrid assembly that resulted in a fluorescence turn-OFF. Streptavidin (strep) was then adsorbed on the QDs-GO-CTAB-AuNP nanohybrid assembly which allowed binding to a biotinylated MNS 4.1 anticocaine DNA aptamer (B) receptor. The addition of cocaine into the strep-B-QDs-GO-CTAB-AuNP aptamer nanoprobe system aided affinity to the aptamer receptor and in turn turned on the fluorescence of the nanoprobe in a concentration-dependent manner. Under optimum experimental conditions, we found the strep-B-QD-GO-CTAB-AuNP to be far superior in its sensitivity to cocaine than the tested strep-B-QDs (no GO and CTAB-AuNPs), strep-B-QD-CTAB-AuNP (no GO) and strep-B-QD-GO (no CTAB-AuNP). In addition, the investigation of localized surface plasmon resonance (LSPR) amplified signal from tested plasmonic NPs shows that CTAB-AuNPs was far superior in amplifying the fluorescence signal of the nanoprobe. A detection limit of 4.6 nM (1.56 ng.mL-1), rapid response time (~2 min) and excellent selectivity against other drugs, substances and cocaine metabolites was achieved. The strep-B-QD-GO-CTAB-AuNP aptamer-based fluorescent nanoprobe was successfully applied for the determination of cocaine in seized adulterated cocaine samples. Graphical abstractSchematic representation of the streptavidin-biotin-quantum dot-graphene oxide-cetyltrimethylammonium bromide-gold nanoparticle aptamer-based fluorescent nanoprobe for cocaine.

Radially and azimuthally polarized laser induced shape transformation of embedded metallic nanoparticles in glass.

Radially and azimuthally polarized picosecond (~10 ps) pulsed laser irradiation at 532 nm wavelength led to the permanent reshaping of spherical silver nanoparticles (~30 - 40 nm in diameter) embedded in a thin layer of soda-lime glass. The observed peculiar shape modifications consist of a number of different orientations of nano-ellipsoids in the cross-section of each written line by laser. A Second Harmonic Generation cross-sectional scan method from silver nanoparticles in transmission geometry was adopted for characterization of the samples after laser modification. The presented approach may lead to sophisticated marking of information in metal-glass nanocomposites.

On the frequency-doubled conically-refracted Gaussian beam.

A Potassium Titanyl Phosphate (KTP) crystal has been used in conjunction with a 10-ps pulsed laser to produce a frequency-doubled conically-refracted Gaussian beam. The 'free' and 'forced' beams that make up the scheme for nonlinear conical refraction were readily observable in non-phase-matched conditions. The dependency of the frequency-doubled beam patterns on the incident beam polarization, which until now has remained unexplored, was examined in detail. We have also revealed the existence of two orthogonally polarized 'free' rays for particular orientations of the incident beam polarization.

Azimuthally and radially polarized light in conical diffraction.

Azimuthal and radial polarization states of light are used to produce conical diffraction (CD) from a KGd(WO4)2 crystal. The patterns produced in the ring plane in each case display marked differences than those seen when linearly polarized incident light is used, with the production of a splitting of the CD ring into two concentric rings of equal intensity. The free space evolution for each type of polarization state is also experimentally recorded and investigated. Comparison with theory shows agreement with the experimentally observed results.

Coherent control of plasmonic nanoantennas using optical eigenmodes.

The last decade has seen subwavelength focusing of the electromagnetic field in the proximity of nanoplasmonic structures with various designs. However, a shared issue is the spatial confinement of the field, which is mostly inflexible and limited to fixed locations determined by the geometry of the nanostructures, which hampers many applications. Here, we coherently address numerically and experimentally single and multiple plasmonic nanostructures chosen from a given array, resorting to the principle of optical eigenmodes. By decomposing the light field into optical eigenmodes, specifically tailored to the nanostructure, we create a subwavelength, selective and dynamic control of the incident light. The coherent control of plasmonic nanoantennas using this approach shows an almost zero crosstalk. This approach is applicable even in the presence of large transmission aberrations, such as present in holographic diffusers and multimode fibres. The method presents a paradigm shift for the addressing of plasmonic nanostructures by light.

P-i-n junction quantum dot saturable absorber mirror: electrical control of ultrafast dynamics.

We report on nonlinear optical properties of a p-i-n junction quantum dot saturable absorber based on InGaAs/GaAs. Absorption recovery dynamics and nonlinear reflectivity are investigated for different reverse bias and pump power conditions. A decrease in absorption recovery time of nearly two orders of magnitude is demonstrated by applying a voltage between 0 and -20 V. The saturable absorber modulation depth and saturation fluence are found to be independent from the applied reverse bias.

Diode-pumped Yb,Er:glass laser passively Q switched with a V3+:YAG crystal.

Saturable-absorber Q switching of a diode-pumped erbium-doped glass laser at 1.54 microm with a V:YAG crystal has been demonstrated. An average output power of 30 mW with Q-switching efficiency of 37% and pulse duration of 350 ns have been obtained. Results of the numerical simulation of the laser have been presented.